JPS6017391B2 - Self-curing coating composition - Google Patents

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention comprises a binder obtained from a blend of an uncatalyzed silicate and an alkyl titanate.
A self-curing, single-pack, inorganic, zinc-rich coating composition.

More specifically, the binder of the present invention is prepared from a low hydrolysis level neutral or alkaline acid alkyl ester mixed with a titanate alkyl ester, which includes the addition of Ti02 and Si02 in a copolymer blend. Approximately 10-6 as Ti02 relative to the total weight
There is 0% by weight of alkyl titanate. Description of the Prior Art Mineral, zinc-rich paints have long been used to protect ferrous metals from corrosion in salt and atmospheric conditions that are not strongly acidic or alkaline.

Zinc-rich paint coating compositions essentially consist of finely divided zinc dust or zinc powder in a porous silicate matrix that provides electrical contact between the zinc dust and the ferrous substrate to provide cathodic protection. Become. Since these coatings were developed and introduced around World War II, research has been directed toward simplifying their handling and application.

Early coatings consisted of zinc dust and aqueous sodium silicate and were cured by baking at high temperatures or by subsequent application of acidic solutions to neutralize the alkali. Later, self-curing coatings were developed that utilized aqueous potassium, lithium or tertiary ammonium silicates as binders. This type of coating would become insoluble upon drying. A second method of providing zinc-rich inorganic paint and coating compositions utilized an organic solvent, usually an alcoholic solution of partially hydrolyzed ethyl lotus acid.

Coating compositions of this type are cured by reaction of the ethyl oxalate binder with atmospheric moisture. ethyl silicate,
Si(OC2K)4, functions as a binder in these reactions.

This is because this ethyl silicate reacts with atmospheric moisture through a two-stage hydrolysis and condensation reaction, as shown in the following formula. Si (OC2 day 5) 40 is 201 Si02 14 C
This reaction is too slow to be of practical use as a coating composition, so the ethyl silicate binder is actually pre-reacted by the addition of an acid stabilizer, and a safe reaction is 80-90 percent. amount of water is required.

Acids, particularly strong stannic acids such as hydrochloric acid or sulfuric acid, catalyze the hydrolysis reaction, possibly causing the silanol hydrolysis products to exist in the brotonic form, which is less reactive than the nucleophilic ionic form, as shown in the equation below. This makes the system metastable. As long as such acids are present, the system will tolerate more than stoichiometric amounts of water and condense slowly.

However, as soon as the acid is neutralized and the system becomes alkaline, gelation occurs rapidly. This is probably because the ionized silanol groups nucleophilically attack the silicon atoms of other silicate or silanol groups to form siloxane bonds, according to the formula below. The acid stabilized binder is then formulated with neutral fillers such as dalc, clay, mica, iron oxide, etc. and additional solvents,
Packaged separately from zinc dust.

Zinc dust is coated immediately before application and reacts with an acid stabilizer,
The mixture is allowed to gel within about 8 to 2 hours. When the liquid mixture is applied to the surface, the solvent evaporates, the acid stabilizer reacts with the zinc or evaporates, and the moisture as atmospheric humidity causes the system to harden. Such prior art zinc-rich coating techniques and compositions therefore suffer from being two-pack materials that require metering, packaging, and mixing immediately prior to application of the coating. It has its drawbacks.

Also, once the individual packages of zinc and carrier composition were mixed, the coating had to be used within a relatively short period of time, usually within 2 to 3 hours.
After the curing time, unused material must be discarded. Other disadvantages of this prior art composition include the sterile packaging and processing required for two-component systems, the time-consuming packaging and mixing;
and the problem of using more than in a given packaging unit. It is desirable to provide an inorganic, zinc-rich, single-pack coating composition that has an acceptable shelf life and is self-curing when exposed to the atmosphere. This has been a long-standing goal in industry. The single-pack, inorganic, zinc-rich paint and coating compositions of the present invention have shelf-life stability and moderate cure rates by using a binder comprised of a mixture of alkyl silicates and alkyl titanates. This goal is achieved by providing a coating composition of the present invention. SUMMARY OF THE INVENTION The present invention provides a self-curing method using a novel binder consisting of an uncatalyzed alkyl silicate mixed with an alkyl titanate and optionally a zinc dust with the desired filler and solvent. The present invention overcomes the limitations and disadvantages of the prior art by providing a single package, mineral, zinc-rich coating composition.

Self-curing copolymer blend of the present invention'MaTi02
and about 10 to 6 weight percent alkyl titanate as TiO2 based on the total weight percent of SiO2. Although there is no upper limit to titanate modification such that packaging stability and acceptable cure rates are reduced, problems with mud cracking begin to occur at levels above 50-6 weight percent. The preferred level is titanate 2 as Tj02 relative to the total weight percent of Ti02 and Si02.
0-4% by weight. The alkyl oxalate component of the new binder has the following formula: Si(OR)40 is 20-Si024ROH (wherein R is ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, and -
(representing an alkyl group selected from the alkyl group consisting of ethylhexyl), the curing of uncatalyzed silicate is utilized.

It is to be understood that the term alkyl lotus acid polymer and other terms for alkyl polymer as used herein is intended to include low molecular weight dimers, trimers, etc. that may be present in the polymer. In a preferred embodiment, an uncatalyzed ethyl silicate such as tetraethylorthosilicate, which is cured in a neutral or alkaline state through a two-stage low-level hydrolysis and condensation reaction as shown in the following formula, is used. . Si (OC2 day 5) 40 is 201 Si02 14
C 2 days 50 days The alkyl titanate component is cured by hydrolysis and condensation reaction in the same way as the alkyl silicate component,
This reaction is carried out by the following formula: Ti(OR) 40 ga Yu→Ti02 0 OH (wherein R'maethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl and 2-
(represents an alkyl group selected from the alkyl group consisting of ethylhexyl).

The alkyl silicate and alkyl titanate components are intermittently mixed with zinc dust or powder to provide a zinc-rich primer or coating composition for ferrous metal substrates.

In addition to zinc, other desired ingredients may be added, such as talc, clay, mica, iron oxide, neutral fillers such as modified pentonite, and other desired fillers, along with additional solvents such as xylene. The alkyl silicate, alkyl titanate copolymer binder containing zinc dust and the desired ingredients exhibits an acceptable shelf life and when used as a coating has the following formula: Mori(OR)40yTi(OR)40 2 (x + y) Hiro○ → (Si02) - an alkyl group selected from the alkyl group consisting essentially of ethylhexyl), it reacts with moisture and hardens.

The curing rate of the aforementioned reaction can be controlled within a predetermined range, since the curing rate increases as the proportion of alkyl titanate in the reaction mixture increases.

As mentioned above, the coating composition according to the present invention has T
It has been found to have a lower level of effectiveness of about 10% titanate as Ti02 relative to the total weight of i02 and Si02. Unlike the prior art, the advantages of the present invention are achieved by mixing alkyl titanates with alkyl silicates using slow hydrolysis and condensation reactions, eliminating acidic or catalyzed alkyl oxalates, resulting in the formation of inorganic , providing a zinc-enriched, single-pack coating composition.

Another feature of the invention is the ability of the new two-component binder to self-cure when exposed to atmospheric moisture.

Other features of the invention include:
It is an object to provide brimer and coating compositions that can withstand saline environments and other corrosive conditions in compositions that are neither strongly acidic nor strongly alkaline.

Other objects and advantages of the invention will become apparent to those skilled in the art from this specification and the description of examples illustrating various features of the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a two-component binder to provide a single-pack, zinc-rich coating composition that cures upon reaction with atmospheric moisture.

The alkyl citrate component, together with the alkyl titanate component,
The present invention is utilized to form a system of copolymers to which zinc dust or zinc powder particles are added to provide a novel zinc-rich coating composition. In a preferred embodiment of the invention, ethyl oxalate, Si(OC2day5)4, is utilized as the uncatalyzed alkyl oxalate. Ethyl silicates not only provide acceptable cure rates when combined with alkyl titanates in accordance with the present invention, but are also commercially attractive given the current market. However, as illustrated by the examples below, the ethyl silicate component alone is not sufficient to provide the benefits of the present invention by utilizing low levels of hydrolysis to provide a stable single packaged component. Although uncatalyzed ethyl oxalate coating compositions may exhibit storage stability, their cure rates are generally unacceptable. Example 1 Ethyl silicate 40 is a mixture of tetraethylorthosilicate and dimers, trimers, etc. and exhibits a hydrolysis level of about 42%.

This ethyl lotus acid contains 40% silica as Si02 and is neither acidic nor alkaline. Ethyl silicate 40
The following compositions were prepared in a laboratory Cowles dispersion hawk. Weight (grams) Materials 160 Ethyl silicate 40 100 Xylene (Kantou Azusa) 170 Clay 3o Modified Pentonite 1200 Zinc dust (pulverized at high speed until completely dispersed, then slowly added to the bottom of the fly) 274 Xylene The composition showed mild pigment settling and good stability when aged for several months, but when applied the film was still wet and flexible after three weeks of curing.

Alkyl orthotitanate, Ti(OR)4, is also similar to silicate ester and undergoes the same hydrolysis and condensation reactions as alkyl silicate.

However, in distinct contrast to alkyl oxalates, alkyl titanates react rapidly with water, and the reaction is almost instantaneous, especially in the case of short-chain alkyl esters. Therefore, when attempting to prepare a stable, single-pack, inorganic, zinc-rich coating composition from alkyl titanates, stable alkyl titanates cure very rapidly, as illustrated in the examples below. Provides an effective coating.
Example 2 The following composition was prepared in a laboratory Cowles dispersion apparatus.

Weight (grams) Materials 272 Tetraptyl titanate 40 Xylene (complete rope frame) 170 Clay 3o Modified pentonite 1200 Zinc dust (pulverized at high speed until completely dispersed, then added slowly with concentration) 228 Xylene This composition exhibited shelf-life stability similar to that of Example 1, but when applied to a steel surface at total OF, 60% relative humidity, this coating composition was dry to the touch within 18 minutes and immediately thereafter Severe mud cracking occurred.

This mud cracking is apparently the result of the surface hardening before all the solvent has evaporated from within the film. Then, as the solvent diffuses and leaches out, the resulting stress is relieved by cracking. According to the invention,
A stable, single-pack, zinc-rich copolymer coating composition is produced by mixing uncatalyzed alkyl silicate with alkyl titanate to form a cobolymer binder.

Blends of alkyl lotus acids and alkyl titanates provide effective binders for stable, zinc-rich, self-curing coating compositions, which have the following formula:
i(OR)40yTi(OR)412(x+y)QO→ (Si02)x (Ti02)y+KOH+WR'OH (wherein R and R are ethyl, n-propyl, isopropyl, n-butyl , isoptyl, secondary purul, and 2-ethylhexyl).

The rate of reactive cure increases as the level of alkyl titanate in the copolymer blend increases proportionally.

It has been found that there is a lower limit level for the effectiveness of alkyl titanates in mixtures. This level of effectiveness is based on the total weight of Ti02 and Si02.
2, the titanate content is approximately 10%. It has been found that there is no upper limit for titanate conversion beyond which packaging stability and acceptable cure rates are reduced. However, at levels above about 50-6 weight percent mud cracking problems begin to occur. The optimal and preferred level is about 20-4% by weight. The following examples show mixed orthosilicates and titanate esters according to the invention,
1 illustrates a typical coating using a novel binder mixture consisting of ethyl silicate and tetrabutyl titanate.

Example 3 A coating composition according to the invention was prepared from the following blends of orthosilicate and titanate ester, ethyl silicate and tetrabutyl titanate.

The above coating composition was applied by conventional spraying and dried to within 19 degrees of humidity at 88 degrees and 60% relative humidity.

After overnight curing, the composition is methyl ethyl ketone (MEK).
) was able to withstand friction caused by cloth filled with it. Compositions ◯ and E showed a tendency to mud cracking, while the others did not. Although low molecular weight silicate polymers or mixtures of orthoesters and timers, trimers, etc. can be used in place of the orthosilicate esters.
It is best to use ortho titanate esters.

This is because the degree of polymerization decreases (0 for orthoester).
), packaging stability increases and titanates are reactive enough to harden rapidly when exposed to humidity.
Example 4 illustrates the use of partially hydrolyzed and condensed ethyl silicate. Example 4 Tetraethyl orthosilicate IJ cate was partially hydrolyzed and condensed (approximately 30%) in the presence of an alkaline catalyst.

Weight (grams) Material 200 Tetraethyl orthosilicate 100 Anhydrous denatured alcohol 9 Deionized water 2 260 Ammonia The mixture was mixed and kept at room temperature for 24 hours.

This was then transferred to a distillation flask and heated to an initial boiling point of 820°C. During the distillation the temperature rose to 160 qo and when the distillation was stopped at this temperature 123 grams of distillate were produced.
The residue has a specific gravity of 0.951, a viscosity of 0.8&ps and 30.
It was a cloudy liquid with 6% Si02. A stable single-pack composition was produced from the distillation residue. weight(
grams) Material 150 Partially hydrolyzed ethyl oxalate 82
Tetraptyl titanate 40 Xylene (Complete Key) 170 Clay 30 Modified Pentonite 1200 Zinc dust (pulverized at high speed until completely dispersed, then slowly added under the fly) 128 Xylene composition within 20 minutes (720F, After drying to the touch (74% relative humidity) and curing overnight, methyl ethyl ketone (74% relative humidity)
M former K).

In Example 4, a hydrolysis operation using ammonia as an alkaline catalyst is described as one method by which partially hydrolyzed low molecular weight polymers are obtained.

Other methods include European hydrolysis as described in US Pat. No. 3,056,684 and the catalytic addition procedure shown in Example 5. Example 5 - Tetra ethyl orthosilicate was partially hydrolyzed and condensed (approximately 42%) according to the following procedure.

Weight (grams) Material 400 Tetraethylorthosilicate Reaction Water Shown.

The hydrolyzed silicate was then used to produce a stable, single-pack, zinc-rich paint.

Weight (grams) Material 256 Partially hydrolyzed ethyl silicate 82
Tetrabutyl titanate (Kankan Toazusa) 170 Clay 3o Modified Pentonite 1200 Zinc dust (pulverized at high speed until completely dispersed, then slowly added under clear water) 202 Xylene composition within 30 minutes (700F, 60% relative After drying to the touch (humidity) and curing overnight, methyl ethyl ketone (
MEK).

As with titanate esters, low molecular weight silicate polymers such as ethyl silicate 40 can also be used to prepare stable, single-pack, zinc-rich primers. Example 6 describes a typical coating composition using an alkyl lotus and alkyl titanate binder to prepare a stable, single-pack, zinc-rich polymer. Example 6 The following series of compositions illustrates the preparation of a typical coating through the use of binders of ethyl silicate 40 and tetrabutyl titanate.

The titanate content is in the range of 20-50% of the total binder as Ti02 + Si02.

The 200% absolute ethanol 35% deionized water mixture was placed in a reaction flask equipped with a hawk frame, heater, and condenser.

This was refluxed at 8 pi for 2 hours and then allowed to cool. When applied by conventional spraying to the surface of unsandblasted steel with 0.85% water or approximately 15% water according to Karl Fischer moisture analysis, all compositions were dissolved within 30 minutes (7
It was so dry that it touched 00F (equivalent to 60% humidity). Only compositions B, C and D were resistant to methyl ethyl ketone (Mold K) after overnight curing. After curing for an additional day, Composition A also became methyl ethyl ketone (MEK) resistant. These compositions exhibit storage stability for at least 6 months and pass the 2000 hour salt spray test (AST).
MB-117) was not affected in any way. The above examples described the use of ethyl silicate and tetrabutyl titanate.

In a preferred embodiment, the ethyl silicate ester is
Because of the availability of ethyl silicate esters from a commercial economic standpoint, they are used as the silicate component in silicate-titanate blends. Other titanate esters are available that function similarly to the butyl titanate used as the alkyl titanate in the copolymer binder of the present invention. Those skilled in the art will appreciate that the reactivity or rate of hydrolysis of other alkyl titanates used in the present invention will depend on the size of the alkyl group. The larger the alkyl group, the slower the rate of hydrolysis. For applications in copolymer binders, the largest alkyl group that meets practical cure rates is 2-ethylhexyl. At the lower limit,
Tetramethyl titanate is solid at room temperature but is insoluble in aromatic solvents. Other esters may be straight or branched, typically ethyl, n-propyl,
These include isopropyl, isobutyl, and secondary butyl. Example 7 illustrates the use of other silicate and titanate esters in copolymer blends. EXAMPLE 7 Alkyl sherates or alkyl zirconylates can be used along with or in place of the alkyl titanate component in the copolymer blends of this invention.

Two alkyl borate compositions were prepared.

One is 20/8 for comparison with alkyl titanate.
A &03/Si02 ratio of 0 was used; the others used trimethylporate as a minor component of the mixed silicate notitanate binder.

The third composition was 30/30% for comparison with alkyl titanates.
It was prepared using an alkyl zirconylate at a Zr02/Si02 ratio of 70. Example 8 illustrates the use of alkyl borates and alkyl zirconylates in copolymer blends of the present invention. Example 8 In Composition A, borate modification enabled the coating to cure, but at a much slower rate than similar levels of titanate.

Claims (1)

Claims: 1. A single package of zinc that has shelf-life stability and is applied to a metal substrate to provide a self-curing, completely mineral coating when exposed to atmospheric moisture. (a) an essentially neutral or alkaline coating composition enriched with a catalyst of the formula: Si(OR)_4(
In the formula, R is ethyl, n-propyl, isopropyl, n-
(b) where the alkyl is ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary and (c) a mixture of zinc powder, with components (a) and (b) acting as a mere binder for said zinc powder. The composition is free of added film-forming organic polymers and the zinc powder is present in sufficient amount to function as an anode and cathodically protect the ferrous substrate coated with the composition. death,
The alkyl titanate is present in the composition in an amount of about 10-60% as TiO_2 based on the total weight of the alkyl titanate and alkyl silicate as TiO_2 and SiO_2, respectively. 2. The composition of claim 1, wherein the amount of alkyl titanate as TiO_2 is about 20 to 40% by weight based on the weight of alkyl titanate and alkyl silicate as TiO_2 and SiO_2, respectively. 3. The composition according to claim 1, wherein the alkyl silicate is partially hydrolyzed tetraethylorthosilicate, the alkyl titanate is tetrabutyl titanate, and the zinc powder is zinc dust. 4. A composition according to claim 1, comprising a liquid vehicle and a neutral filler. 5. The composition of claim 4, wherein the vehicle is xylene and the filler is clay.